This invention relates to a method and apparatus for acoustic ink printing using a bilayer configuration. More particularly, the invention concerns an acoustically actuated droplet emitter device which is provided with a continuous, high velocity, laminar flow of cooling liquid in addition to a stagnant pool of liquid to be emitted as droplets.
While the invention is particularly directed to the art of acoustic ink printing, and will be thus described with specific reference thereto, it will be appreciated that the invention may have usefulness in other fields and applications. For example, the invention may be used in other acoustic wave generators wherein other types of fluid such as molten metal, etc. are emitted using an array of emitters.
By way of background, acoustic droplet emitters are known in the art and use focussed acoustic energy to emit droplets of fluid. Acoustic droplet emitters are useful in a variety of applications due to the wide range of fluids that can be emitted as droplets. For instance, if marking fluids are used the acoustic droplet emitter can be employed as a printhead in a printer. Acoustic droplet emitters do not use nozzles, which are prone to clogging, to control droplet size and volume, and many other fluids may also be used in an acoustic droplet emitter making it useful for a variety of applications. For instance, it is stated in U.S. Pat. No. 5,565,113 issued Oct. 15, 1996 by Hadimioglu et al. titled xe2x80x9cLithographically Defined Ejection Unitsxe2x80x9d and incorporated by reference herein, that mylar catalysts, molten solder, hot melt waxes, color filter materials, resists and chemical and biological compounds are all feasible materials to be used in an acoustic droplet emitter.
One issue when using high-viscosity fluids in an acoustic droplet emitter is the high attenuation of acoustic energy in high-viscosity fluids. High attenuation rates may therefore require larger amounts of acoustic power to achieve droplet emission from high-viscosity fluids. One solution to this problem has been shown in U.S. Pat. No. 5,565,113 issued Oct. 15, 1996 by Hadimioglu et al. titled xe2x80x9cLithographically Defined Ejection Unitsxe2x80x9d and incorporated by reference hereinabove and is shown in FIG. 1.
FIG. 1 shows a cross-sectional view of an individual droplet emitter 10 for an acoustically actuated printer such as is shown in U.S. Pat. No. 5,565,113 by Hadimioglu et al. titled xe2x80x9cLithographically Defined Ejection Unitsxe2x80x9d and incorporated by reference hereinabove. The droplet emitter 10 has a base substrate 12 with a transducer 16 interposed between two electrodes 17 on one surface and an acoustic lens 14 on an opposite surface. Attached to the same side of the base substrate 12 as the acoustic lens is a top support 18 with a liquid cell 22, defined by sidewalls 20, which holds a low attenuation liquid 23. Supported by the top support 18 is an acoustically thin capping structure 26 which forms the top surface of the liquid cell 22 and seals in the low attenuation liquid 23.
The droplet emitter 10 further includes a reservoir 24, located over the acoustically thin capping structure 26, which holds emission fluid 32. As shown in FIG. 1, the reservoir 24 includes an aperture 30 defined by sidewalls 34. The sidewalls 34 include a plurality of portholes 36 through which the emission fluid 32 passes. A pressure means forces the emission fluid 32 through the portholes 36 so as to create a pool of emission fluid 32 having a free surface 28 over the acoustically thin capping structure 26.
The transducer 16, acoustic lens 14, and aperture 30 are all axially aligned such that an acoustic wave produced by the transducer 16 will be focussed by its aligned acoustic lens 14 at approximately the free surface 28 of the emission fluid 32 in its aligned aperture 30. When sufficient power is obtained, a mound 38 is formed and a droplet 39 is emitted from the mound 38. The acoustic energy readily passes through the acoustically thin capping structure 26 and the low attenuation liquid 23. By maintaining only a very thin pool of emission fluid 32 acoustic energy loss due to the high attenuation rate of the emission fluid 32 is minimized.
FIG. 2 shows a perspective view of two arrays of the droplet emitter 10 shown in FIG. 1. The arrays 31 of apertures 30 can be clearly above the two reservoirs 24. Each array 31 has a width W and a length L where the length L of the array 24 is the larger of the two dimensions. Having arrays of droplet emitters 10 is useful, for instance, to enable a color printing application where each array might be associated with a different colored ink. This configuration of the arrays allows for accurate location of each individual droplet emitter 10 and precise alignment of the arrays 31 relative to each other which increases, among other things droplet placement accuracy.
However, the low attenuation liquid 23, the emission fluid 32, and the substrate 12 will heat up from the portion of the acoustic energy that is absorbed in the low attenuation liquid 23, the emission fluid 32, and the substrate 12 which is not transferred to the kinetic and surface energy of the emitted drops 39. This will in turn cause excess heating of the emission fluid 32. The emission fluid 32 can sustain temperature increases by only a few degrees centigrade before emitted droplets show drop misplacement on the receiving media. In a worst case scenario, the low attenuation liquid 23 can absorb enough energy to cause it to boil and to destroy the droplet emitter 10. The practical consequences of this are that the emission speed must be kept very slow to prevent the low attenuation liquid 23 from absorbing too much excess energy in a short time period and heating up to unacceptable levels.
Therefore, it would be highly desirable if a droplet emitter 10 could be designed to operate while maintaining a uniform thermal operating temperature at high emission speeds. One such prior approach is described in U.S. Pat. No. 6,134,291, filed Jul. 23, 1999 (and issued Oct. 17, 2000) and entitled xe2x80x9cAn Acoustic Ink Jet Printhead Design and Method of Operation Utilizing Flowing Coolant and an Emission Fluid,xe2x80x9d which is incorporated herein by reference.
As described therein, turning now to FIG. 3, there is shown a cross-sectional view of a droplet emitter 40. The droplet emitter 40 has a base substrate 42 with transducers 46 on one surface and acoustic lenses 44 on an opposite surface. Spaced from the base substrate 42 is an acoustically thin capping structure 50. The acoustically thin capping structure 50 may be either a rigid structure made from, for example, silicon, or a membrane structure made from, for example, parylene, mylar, or kapton. In order to preserve the acoustic transmission properties the acoustically thin capping structure 50 should preferably have either a very thin thickness such as approximately {fraction (1/10)}th of the wavelength of the transmitted acoustic energy in the membrane material or a thickness substantially equal to a multiple of one-half the wavelength of the transmitted acoustic energy in the membrane material. Whether the acoustically thin capping structure 50 is made from a rigid material or a membrane it will structurally be relatively thin and have a tendency to be fragile and susceptible to breakage. To provide additional stability for the acoustically thin capping structure 50 it is supported by a capping structure support 51. The capping structure support 51 is interposed between the base substrate 42 and the acoustically thin capping structure 50, adjacent to the acoustically thin capping structure 50 and spaced from the base substrate 42. The capping structure support 51 has a series of spaced apart apertures 49, positioned in a like manner to lens array 44, so that focussed acoustic energy may pass by the capping structure support 51 substantially unimpeded. The apertures 49 have a capping structure support aperture diameter d1. The addition of the capping structure support 51 allows for a wider variety of materials to be used as the acoustically thin capping structure 50 and adds strength and stability to the acoustically thin capping structure 50.
The chamber created by the space between the base substrate 42 and the acoustically thin capping structure 50 is filled with a low attenuation fluid 52. The chamber could be filled with the low attenuation fluid 52 and sealed as described hereinabove with respect to FIG. 1, however, benefits can be achieved if the chamber is not sealed and the low attenuation fluid 52 is allowed to flow through the chamber. FIG. 3 shows a flow direction of the low attenuation fluid F2 which is orthogonal to the plane of the drawing and out of the plane of the drawing. However, while a droplet emitter 40 which has a flow direction of the low attenuation fluid F2 in this direction may possibly be the easiest to construct, other flow directions are possible and may even in some circumstances be preferable. For instance, the droplet emitter 40 could also be constructed such that the flow direction of the low attenuation fluid F2 was flowing in the plane of the drawing in either a xe2x80x9crightxe2x80x9d or xe2x80x9cleftxe2x80x9d direction.
Flowing the low attenuation liquid 52 enables the low attenuation liquid 52 to help maintain thermal uniformity of the droplet emitter 40. In particular, not only does the low attenuation liquid 52 itself have less opportunity to heat up due to excess heat generated during the acoustic emission process but because the low attenuation liquid 52 is in thermal contact with the substrate 42 the low attenuation liquid 52 may also absorb excess heat generated in the substrate 42 during operation and prevent excess heating of the substrate 42 as well. Further, it can be appreciated that this structure of a thin capping structure over a relatively rigid capping support creates a fluidically sealed flow chamber enabling relatively high flow rates of the low attenuation fluid without changing the position of the capping structure with respect to the focussed acoustic beam. Consequently, rapid removal of excess generated heat and temperature uniformity is achieved.
Spaced from the acoustically thin capping structure 50 is a liquid level control plate 56. The acoustically thin capping structure 50 and the liquid level control plate 56 define a channel which holds an emission fluid 48. The liquid level control plate 56 contains an array 54 of apertures 60. The transducers 46, acoustic lenses 44, apertures 49 and apertures 60 are all axially aligned such that an acoustic wave produced by a single transducer 46 will be focussed by its aligned acoustic lens 44 at approximately a free surface 58 of the emission fluid 48 in its aligned aperture 60. When sufficient power is obtained, a droplet is emitted. It should be noted that the apertures 60 in the liquid level control plate 56 have a liquid level control plate aperture diameter d2. In order to insure that the acoustic wave produced by a transducer will propagate substantially unimpeded through the aperture 49 in the capping structure support aperture diameter d1 should be larger than the diameter of the acoustic beam as it passes through the aperture 49.
FIG. 4 shows a perspective view of the droplet emitter 40 shown in FIG. 3. The array 54 of apertures 60 can be clearly seen on the liquid level control plate 56. The flow direction of the low attenuation fluid F2 between the base substrate 42 and the acoustically thin capping structure 50 can be clearly seen as well as the flow direction of the emission fluid F1 between the acoustically thin capping structure 50 and the liquid level control plate 56. In FIG. 4, a length L and a width W of the array 54 can also be seen and the width W is the smaller dimension. The flow direction of the emission fluid F1 is arranged such that the emission fluid 48 flows along the shorter width W of the array 54 instead of along the longer length L of the array 54. When the flow direction of the emission fluid F1 is arranged to be orthogonal to the flow direction of the low attenuation fluid F2, then it is preferable to arrange the flow direction of the emission fluid F1 such that the emission fluid 48 flows along the shorter width W of the array 54 instead of along the longer length L because the emission fluid is more sensitive to constraining factors. For instance, small pressure deviations in the emission fluid 48 along the array 54 can lead to misdirectionality of the emitted droplets. However, in this configuration, the flow velocity of the emission fluid 48 is substantially independent of many of the constraining factors.
If, however, the droplet emitter 40 is constructed such that the flow direction of the emission fluid F1 and the flow direction of the low attenuation fluid F2 are substantially parallel instead of orthogonal to each other, then it is preferable that both the flow direction of the emission fluid F1 and the flow direction of the low attenuation fluid F2 be along the width of the array for the reasons stated above.
FIG. 5 shows a cross-sectional view of how the droplet emitter of FIGS. 3 and 4 can be assembled with a fluid manifold 62 to provide the emission fluid 48 to the droplet emitter. While unitary construction of the fluid manifold 62 may in some circumstances be desirable, in this implementation the fluid manifold 62 is divided into two portions, an upper manifold 98 and a lower manifold 92 with a flexible seal 84 therebetween.
The lower manifold 92 has a liquid level control gap protrusion 94. The liquid level control plate 56 is attached to a liquid level control gap protrusion 94. The liquid level control gap protrusion 94 is used to achieve a precise spacing between the base substrate 42 and the liquid level control plate 56 when the parts are assembled into the droplet emitter 40 and attached to the lower manifold 92.
An additional part assembled with the lower manifold 92 and the droplet emitter stack 40 is a bridge plate 82 as shown in FIG. 6. The bridge plate 82 is used to mount a flex cable 100. The flex cable 100 is used to provide connections for discrete circuit components 76 which are mounted on the flex cable 100 and are used to generate and control the focussed acoustic wave. Bond wires 96 provide electrical connections between the flex cable 100 and circuit chips 80 mounted on the base substrate 42. Control circuitry for the droplet emitter is described for instance in U.S. Pat. No. 5,786,722 by Buhler et al. titled xe2x80x9cIntegrated RF Switching Cell Built In CMOS Technology And Utilizing A High Voltage Integrated Circuit Diode With A Charge Injecting Nodexe2x80x9d issued Jul. 28, 1998, or U.S. Pat. No. 5,389,956 by Hadimioglu et al. titled xe2x80x9cTechniques For Improving Droplet Uniformity In Acoustic Ink Printingxe2x80x9d issued Feb. 14, 1995, both incorporated by reference herein.
FIG. 6 shows a cross-sectional view of how the droplet emitter of FIGS. 3 and 4 can be assembled with a fluid manifold 62 to provide the low attenuation fluid 52 to the droplet emitter. While unitary construction of the fluid manifold 62 may in some circumstances be desirable, in this implementation the fluid manifold 62 is again divided into two portions as described hereinabove, an upper manifold 98 and a lower manifold 92 with a flexible seal 84 therebetween.
The capping support plate 51 is positioned below the substrate 42 and sealed around the substrate in a manner such as to achieve a precise spacing between the base substrate 42 and the acoustically thin capping structure 50 when the parts are assembled into the droplet emitter 40 and attached to the lower manifold 92.
The assembly of the droplet emitter 40 and attachment to the fluid manifold 62 creates a liquid flow chamber 128 starting at the manifold inlet 120, proceeding through the gap between the base substrate 42 and the acoustically thin capping structure 50 and ending at the manifold outlet 122.
However, none of these known acoustic ink printhead configurations allow for a flowing coolant to maintain the thermal integrity of the system and an ink reservoir that does not require continuous flow. Such a configuration is desirable because the advantages of using both high viscosity inks (which do not readily flow) and flowing coolant could then be realized in a single advantageous application.
The present invention contemplates a new and improved acoustic ink printhead that attains the desired configuration and resolves the above-referenced difficulties and others.
A method and apparatus for acoustic ink printing using a bilayer printhead configuration are provided.
In one aspect of the invention, a droplet emitter device comprises a substrate having a first array of acoustic wave focussing devices positioned thereon, a plate having a second array of orifices disposed therein, the second array being aligned with the first array such that each focussing device is aligned with an orifice, a membrane positioned between the plate and the substrate, a first fluid chamber defined by the substrate and the membrane, the first fluid chamber being disposed to facilitate continuous flow of a first fluid across the first array and a second fluid chamber defined by the membrane and the plate, the second fluid chamber being disposed to maintain a stagnant volume of second fluid, the volume remaining stagnant until the second fluid is drawn from a supply upon emission of droplets of the second fluid through the orifices, such emission being dependent on generation and focussing of acoustic waves by corresponding focussing devices of the first array.
In another aspect of the invention, the first fluid is coolant.
In another aspect of the invention, the second fluid is ink.
In another aspect of the invention, a droplet emitter device comprises a substrate having a first array of lenses positioned thereon, a plate having a second array of orifices disposed therein, the second array being aligned with the first array such that each lens is aligned with an orifice, an acoustically thin membrane positioned between the plate and the substrate, a first fluid chamber defined by the substrate and the membrane, the first fluid chamber being disposed to facilitate continuous flow of a coolant across the first array and a second fluid chamber defined by the membrane and the plate, the second fluid chamber being disposed to maintain a stagnant volume of ink, the volume remaining stagnant until the ink fluid is drawn from a supply upon emission of droplets of the ink through the orifices, such emission being dependent on generation and focussing of acoustic waves by corresponding lenses of the first array.
In another aspect of the invention, a method comprises steps of facilitating a continuous flow of a coolant in the first chamber across the first array, maintaining a stagnant volume of ink in the second fluid chamber and drawing ink into the second chamber upon emission of droplets of the ink through the orifices, such emission being dependent on generation and focussing of acoustic waves by corresponding lenses of the first array.
Further scope of the applicability of the present invention will become apparent from the detailed description provided below. It should be understood, however, that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art.